From cc1229e75e0c0c2cf5ae6d67bc7411c2631deb86 Mon Sep 17 00:00:00 2001
From: Vincent Vanlaer <vincent.vanlaer@skynet.be>
Date: Thu, 1 Feb 2018 20:27:35 +0100
Subject: [PATCH 1/8] Add atomic gamma setting

---
 backend/drm/atomic.c             | 32 ++++++++++++++++++++++++++++++++
 backend/drm/drm.c                |  5 ++++-
 backend/drm/legacy.c             |  8 ++++++++
 backend/drm/properties.c         |  1 +
 include/backend/drm/drm.h        |  5 ++++-
 include/backend/drm/iface.h      |  4 ++++
 include/backend/drm/properties.h |  3 ++-
 7 files changed, 55 insertions(+), 3 deletions(-)

diff --git a/backend/drm/atomic.c b/backend/drm/atomic.c
index 54024d86..a8003492 100644
--- a/backend/drm/atomic.c
+++ b/backend/drm/atomic.c
@@ -1,3 +1,4 @@
+#include <stdlib.h>
 #include <gbm.h>
 #include <xf86drm.h>
 #include <xf86drmMode.h>
@@ -195,9 +196,40 @@ static bool atomic_crtc_move_cursor(struct wlr_drm_backend *drm,
 	return atomic_end(drm->fd, &atom);
 }
 
+static bool atomic_crtc_set_gamma(struct wlr_drm_backend *drm,
+		struct wlr_drm_crtc *crtc, uint16_t *r, uint16_t *g, uint16_t *b,
+		uint32_t size) {
+	struct drm_color_lut *gamma = calloc(sizeof(struct drm_color_lut), size);
+
+	for (uint32_t i = 0; i < size; i++) {
+		gamma[i].red = r[i];
+		gamma[i].green = g[i];
+		gamma[i].blue = b[i];
+	}
+
+	if (crtc->gamma_lut != 0) {
+		drmModeDestroyPropertyBlob(drm->fd, crtc->gamma_lut);
+	}
+
+	if (drmModeCreatePropertyBlob(drm->fd, gamma,
+				sizeof(struct drm_color_lut) * size, &crtc->gamma_lut)) {
+		wlr_log_errno(L_ERROR, "Unable to create property blob");
+		return false;
+	}
+
+	free(gamma);
+
+	struct atomic atom;
+
+	atomic_begin(crtc, &atom);
+	atomic_add(&atom, crtc->id, crtc->props.gamma_lut, crtc->gamma_lut);
+	return atomic_end(drm->fd, &atom);
+}
+
 const struct wlr_drm_interface atomic_iface = {
 	.conn_enable = atomic_conn_enable,
 	.crtc_pageflip = atomic_crtc_pageflip,
 	.crtc_set_cursor = atomic_crtc_set_cursor,
 	.crtc_move_cursor = atomic_crtc_move_cursor,
+	.crtc_set_gamma = atomic_crtc_set_gamma,
 };
diff --git a/backend/drm/drm.c b/backend/drm/drm.c
index 08ced783..abcfcf8a 100644
--- a/backend/drm/drm.c
+++ b/backend/drm/drm.c
@@ -169,6 +169,9 @@ void wlr_drm_resources_free(struct wlr_drm_backend *drm) {
 		if (crtc->mode_id) {
 			drmModeDestroyPropertyBlob(drm->fd, crtc->mode_id);
 		}
+		if (crtc->gamma_lut) {
+			drmModeDestroyPropertyBlob(drm->fd, crtc->gamma_lut);
+		}
 	}
 	for (size_t i = 0; i < drm->num_planes; ++i) {
 		struct wlr_drm_plane *plane = &drm->planes[i];
@@ -227,7 +230,7 @@ static void wlr_drm_connector_set_gamma(struct wlr_output *output,
 		uint32_t size, uint16_t *r, uint16_t *g, uint16_t *b) {
 	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
 	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
-	drmModeCrtcSetGamma(drm->fd, conn->crtc->id, size, r, g, b);
+	drm->iface->crtc_set_gamma(drm, conn->crtc, r, g, b, size);
 }
 
 static uint32_t wlr_drm_connector_get_gamma_size(struct wlr_output *output) {
diff --git a/backend/drm/legacy.c b/backend/drm/legacy.c
index 61140cec..46911905 100644
--- a/backend/drm/legacy.c
+++ b/backend/drm/legacy.c
@@ -59,9 +59,17 @@ bool legacy_crtc_move_cursor(struct wlr_drm_backend *drm,
 	return !drmModeMoveCursor(drm->fd, crtc->id, x, y);
 }
 
+bool legacy_crtc_set_gamma(struct wlr_drm_backend *drm,
+		struct wlr_drm_crtc *crtc, uint16_t *r, uint16_t *g, uint16_t *b,
+		uint32_t size) {
+	return !drmModeCrtcSetGamma(drm->fd, crtc->id, size, r, g, b);
+}
+
+
 const struct wlr_drm_interface legacy_iface = {
 	.conn_enable = legacy_conn_enable,
 	.crtc_pageflip = legacy_crtc_pageflip,
 	.crtc_set_cursor = legacy_crtc_set_cursor,
 	.crtc_move_cursor = legacy_crtc_move_cursor,
+	.crtc_set_gamma = legacy_crtc_set_gamma,
 };
diff --git a/backend/drm/properties.c b/backend/drm/properties.c
index 5bec3243..c3efa96e 100644
--- a/backend/drm/properties.c
+++ b/backend/drm/properties.c
@@ -28,6 +28,7 @@ static const struct prop_info connector_info[] = {
 static const struct prop_info crtc_info[] = {
 #define INDEX(name) (offsetof(union wlr_drm_crtc_props, name) / sizeof(uint32_t))
 	{ "ACTIVE",       INDEX(active) },
+	{ "GAMMA_LUT",    INDEX(gamma_lut) },
 	{ "MODE_ID",      INDEX(mode_id) },
 	{ "rotation",     INDEX(rotation) },
 	{ "scaling mode", INDEX(scaling_mode) },
diff --git a/include/backend/drm/drm.h b/include/backend/drm/drm.h
index af472ede..782764c8 100644
--- a/include/backend/drm/drm.h
+++ b/include/backend/drm/drm.h
@@ -39,7 +39,10 @@ struct wlr_drm_plane {
 
 struct wlr_drm_crtc {
 	uint32_t id;
-	uint32_t mode_id; // atomic modesetting only
+
+	// Atomic modesetting only
+	uint32_t mode_id;
+	uint32_t gamma_lut;
 	drmModeAtomicReq *atomic;
 
 	union {
diff --git a/include/backend/drm/iface.h b/include/backend/drm/iface.h
index 4a5d2e9d..228b313a 100644
--- a/include/backend/drm/iface.h
+++ b/include/backend/drm/iface.h
@@ -27,6 +27,10 @@ struct wlr_drm_interface {
 	// Move the cursor on crtc
 	bool (*crtc_move_cursor)(struct wlr_drm_backend *drm,
 		struct wlr_drm_crtc *crtc, int x, int y);
+	// Set the gamma lut on crtc
+	bool (*crtc_set_gamma)(struct wlr_drm_backend *drm,
+			struct wlr_drm_crtc *crtc, uint16_t *r, uint16_t *g, uint16_t *b,
+			uint32_t size);
 };
 
 extern const struct wlr_drm_interface atomic_iface;
diff --git a/include/backend/drm/properties.h b/include/backend/drm/properties.h
index 7de386ea..119d24c3 100644
--- a/include/backend/drm/properties.h
+++ b/include/backend/drm/properties.h
@@ -32,8 +32,9 @@ union wlr_drm_crtc_props {
 
 		uint32_t active;
 		uint32_t mode_id;
+		uint32_t gamma_lut;
 	};
-	uint32_t props[4];
+	uint32_t props[5];
 };
 
 union wlr_drm_plane_props {

From ab011406add31c518f6f352189b1dc6246a74fdb Mon Sep 17 00:00:00 2001
From: Vincent Vanlaer <vincent.vanlaer@skynet.be>
Date: Sun, 4 Feb 2018 21:03:44 +0100
Subject: [PATCH 2/8] Add atomic gamma lut size fetching

Legacy gamma lut size now uses the new legacy_crtc member of
wlr_drm_crtc. This was Previously doen using old_crtc in
wlr_drm_connector, but since this refers to the crtc that was connected to
the ouput, this could give the wrong result.
---
 backend/drm/atomic.c             | 14 ++++++++++++++
 backend/drm/drm.c                |  6 ++++--
 backend/drm/legacy.c             |  5 +++++
 backend/drm/properties.c         | 11 ++++++-----
 include/backend/drm/drm.h        |  3 +++
 include/backend/drm/iface.h      |  3 +++
 include/backend/drm/properties.h |  3 ++-
 7 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/backend/drm/atomic.c b/backend/drm/atomic.c
index a8003492..79765fef 100644
--- a/backend/drm/atomic.c
+++ b/backend/drm/atomic.c
@@ -226,10 +226,24 @@ static bool atomic_crtc_set_gamma(struct wlr_drm_backend *drm,
 	return atomic_end(drm->fd, &atom);
 }
 
+static uint32_t atomic_crtc_get_gamma_size(struct wlr_drm_backend *drm,
+		struct wlr_drm_crtc *crtc) {
+	uint64_t gamma_lut_size;
+
+	if (!wlr_drm_get_prop(drm->fd, crtc->id, crtc->props.gamma_lut_size,
+			   &gamma_lut_size)) {
+		wlr_log(L_ERROR, "Unable to get gamma lut size");
+		return 0;
+	}
+
+	return (uint32_t) gamma_lut_size;
+}
+
 const struct wlr_drm_interface atomic_iface = {
 	.conn_enable = atomic_conn_enable,
 	.crtc_pageflip = atomic_crtc_pageflip,
 	.crtc_set_cursor = atomic_crtc_set_cursor,
 	.crtc_move_cursor = atomic_crtc_move_cursor,
 	.crtc_set_gamma = atomic_crtc_set_gamma,
+	.crtc_get_gamma_size = atomic_crtc_get_gamma_size,
 };
diff --git a/backend/drm/drm.c b/backend/drm/drm.c
index abcfcf8a..eef1e333 100644
--- a/backend/drm/drm.c
+++ b/backend/drm/drm.c
@@ -140,6 +140,7 @@ bool wlr_drm_resources_init(struct wlr_drm_backend *drm) {
 	for (size_t i = 0; i < drm->num_crtcs; ++i) {
 		struct wlr_drm_crtc *crtc = &drm->crtcs[i];
 		crtc->id = res->crtcs[i];
+		crtc->legacy_crtc = drmModeGetCrtc(drm->fd, crtc->id);
 		wlr_drm_get_crtc_props(drm->fd, crtc->id, &crtc->props);
 	}
 
@@ -166,6 +167,7 @@ void wlr_drm_resources_free(struct wlr_drm_backend *drm) {
 	for (size_t i = 0; i < drm->num_crtcs; ++i) {
 		struct wlr_drm_crtc *crtc = &drm->crtcs[i];
 		drmModeAtomicFree(crtc->atomic);
+		drmModeFreeCrtc(crtc->legacy_crtc);
 		if (crtc->mode_id) {
 			drmModeDestroyPropertyBlob(drm->fd, crtc->mode_id);
 		}
@@ -235,8 +237,8 @@ static void wlr_drm_connector_set_gamma(struct wlr_output *output,
 
 static uint32_t wlr_drm_connector_get_gamma_size(struct wlr_output *output) {
 	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
-	drmModeCrtc *crtc = conn->old_crtc;
-	return crtc ? crtc->gamma_size : 0;
+	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
+	return drm->iface->crtc_get_gamma_size(drm, conn->crtc);
 }
 
 void wlr_drm_connector_start_renderer(struct wlr_drm_connector *conn) {
diff --git a/backend/drm/legacy.c b/backend/drm/legacy.c
index 46911905..eec8c642 100644
--- a/backend/drm/legacy.c
+++ b/backend/drm/legacy.c
@@ -65,6 +65,10 @@ bool legacy_crtc_set_gamma(struct wlr_drm_backend *drm,
 	return !drmModeCrtcSetGamma(drm->fd, crtc->id, size, r, g, b);
 }
 
+uint32_t legacy_crtc_get_gamma_size(struct wlr_drm_backend *drm,
+		struct wlr_drm_crtc *crtc) {
+	return crtc->legacy_crtc->gamma_size;
+}
 
 const struct wlr_drm_interface legacy_iface = {
 	.conn_enable = legacy_conn_enable,
@@ -72,4 +76,5 @@ const struct wlr_drm_interface legacy_iface = {
 	.crtc_set_cursor = legacy_crtc_set_cursor,
 	.crtc_move_cursor = legacy_crtc_move_cursor,
 	.crtc_set_gamma = legacy_crtc_set_gamma,
+	.crtc_get_gamma_size = legacy_crtc_get_gamma_size,
 };
diff --git a/backend/drm/properties.c b/backend/drm/properties.c
index c3efa96e..153e845e 100644
--- a/backend/drm/properties.c
+++ b/backend/drm/properties.c
@@ -27,11 +27,12 @@ static const struct prop_info connector_info[] = {
 
 static const struct prop_info crtc_info[] = {
 #define INDEX(name) (offsetof(union wlr_drm_crtc_props, name) / sizeof(uint32_t))
-	{ "ACTIVE",       INDEX(active) },
-	{ "GAMMA_LUT",    INDEX(gamma_lut) },
-	{ "MODE_ID",      INDEX(mode_id) },
-	{ "rotation",     INDEX(rotation) },
-	{ "scaling mode", INDEX(scaling_mode) },
+	{ "ACTIVE",         INDEX(active) },
+	{ "GAMMA_LUT",      INDEX(gamma_lut) },
+	{ "GAMMA_LUT_SIZE", INDEX(gamma_lut_size) },
+	{ "MODE_ID",        INDEX(mode_id) },
+	{ "rotation",       INDEX(rotation) },
+	{ "scaling mode",   INDEX(scaling_mode) },
 #undef INDEX
 };
 
diff --git a/include/backend/drm/drm.h b/include/backend/drm/drm.h
index 782764c8..12530da6 100644
--- a/include/backend/drm/drm.h
+++ b/include/backend/drm/drm.h
@@ -45,6 +45,9 @@ struct wlr_drm_crtc {
 	uint32_t gamma_lut;
 	drmModeAtomicReq *atomic;
 
+	// Legacy only
+	drmModeCrtc *legacy_crtc;
+
 	union {
 		struct {
 			struct wlr_drm_plane *overlay;
diff --git a/include/backend/drm/iface.h b/include/backend/drm/iface.h
index 228b313a..15cdf1ab 100644
--- a/include/backend/drm/iface.h
+++ b/include/backend/drm/iface.h
@@ -31,6 +31,9 @@ struct wlr_drm_interface {
 	bool (*crtc_set_gamma)(struct wlr_drm_backend *drm,
 			struct wlr_drm_crtc *crtc, uint16_t *r, uint16_t *g, uint16_t *b,
 			uint32_t size);
+	// Get the gamma lut size of a crtc
+	uint32_t (*crtc_get_gamma_size)(struct wlr_drm_backend *drm,
+			struct wlr_drm_crtc *crtc);
 };
 
 extern const struct wlr_drm_interface atomic_iface;
diff --git a/include/backend/drm/properties.h b/include/backend/drm/properties.h
index 119d24c3..3cf8cc87 100644
--- a/include/backend/drm/properties.h
+++ b/include/backend/drm/properties.h
@@ -33,8 +33,9 @@ union wlr_drm_crtc_props {
 		uint32_t active;
 		uint32_t mode_id;
 		uint32_t gamma_lut;
+		uint32_t gamma_lut_size;
 	};
-	uint32_t props[5];
+	uint32_t props[6];
 };
 
 union wlr_drm_plane_props {

From f5e5d1983b96f848ed89bdd3b0ea9825efa75063 Mon Sep 17 00:00:00 2001
From: Vincent Vanlaer <vincent.vanlaer@skynet.be>
Date: Sun, 4 Feb 2018 21:50:52 +0100
Subject: [PATCH 3/8] Do not allow gamma control without a crtc

---
 backend/drm/drm.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/backend/drm/drm.c b/backend/drm/drm.c
index eef1e333..70e6a1cf 100644
--- a/backend/drm/drm.c
+++ b/backend/drm/drm.c
@@ -232,13 +232,21 @@ static void wlr_drm_connector_set_gamma(struct wlr_output *output,
 		uint32_t size, uint16_t *r, uint16_t *g, uint16_t *b) {
 	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
 	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
-	drm->iface->crtc_set_gamma(drm, conn->crtc, r, g, b, size);
+
+	if (conn->crtc) {
+		drm->iface->crtc_set_gamma(drm, conn->crtc, r, g, b, size);
+	}
 }
 
 static uint32_t wlr_drm_connector_get_gamma_size(struct wlr_output *output) {
 	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
 	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
-	return drm->iface->crtc_get_gamma_size(drm, conn->crtc);
+
+	if (conn->crtc) {
+		return drm->iface->crtc_get_gamma_size(drm, conn->crtc);
+	}
+
+	return 0;
 }
 
 void wlr_drm_connector_start_renderer(struct wlr_drm_connector *conn) {

From 2df97ed16aa66f2e5f54b847b4389d4b1af5cc40 Mon Sep 17 00:00:00 2001
From: Vincent Vanlaer <vincent.vanlaer@skynet.be>
Date: Fri, 9 Feb 2018 17:14:36 +0100
Subject: [PATCH 4/8] Set needs_swap on output when gamma changes

---
 backend/drm/drm.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/backend/drm/drm.c b/backend/drm/drm.c
index 70e6a1cf..15be16bc 100644
--- a/backend/drm/drm.c
+++ b/backend/drm/drm.c
@@ -232,10 +232,15 @@ static void wlr_drm_connector_set_gamma(struct wlr_output *output,
 		uint32_t size, uint16_t *r, uint16_t *g, uint16_t *b) {
 	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
 	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
+	bool ok;
 
 	if (conn->crtc) {
-		drm->iface->crtc_set_gamma(drm, conn->crtc, r, g, b, size);
+		ok = drm->iface->crtc_set_gamma(drm, conn->crtc, r, g, b, size);
+		if (ok) {
+			wlr_output_update_needs_swap(output);
+		}
 	}
+
 }
 
 static uint32_t wlr_drm_connector_get_gamma_size(struct wlr_output *output) {

From b2f69416178d84e686e9024a262eaa1e18fdb966 Mon Sep 17 00:00:00 2001
From: Vincent Vanlaer <vincent.vanlaer@skynet.be>
Date: Fri, 9 Feb 2018 17:48:17 +0100
Subject: [PATCH 5/8] Free gamma when property blob creation fails

---
 backend/drm/atomic.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/backend/drm/atomic.c b/backend/drm/atomic.c
index 79765fef..164caf22 100644
--- a/backend/drm/atomic.c
+++ b/backend/drm/atomic.c
@@ -214,6 +214,7 @@ static bool atomic_crtc_set_gamma(struct wlr_drm_backend *drm,
 	if (drmModeCreatePropertyBlob(drm->fd, gamma,
 				sizeof(struct drm_color_lut) * size, &crtc->gamma_lut)) {
 		wlr_log_errno(L_ERROR, "Unable to create property blob");
+		free(gamma);
 		return false;
 	}
 

From 0232269a2d92e76dfe20cfbde0646798ab080e95 Mon Sep 17 00:00:00 2001
From: Vincent Vanlaer <vincent.vanlaer@skynet.be>
Date: Fri, 9 Feb 2018 19:35:44 +0100
Subject: [PATCH 6/8] Fix style

---
 backend/drm/atomic.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/backend/drm/atomic.c b/backend/drm/atomic.c
index 164caf22..10714e35 100644
--- a/backend/drm/atomic.c
+++ b/backend/drm/atomic.c
@@ -221,7 +221,6 @@ static bool atomic_crtc_set_gamma(struct wlr_drm_backend *drm,
 	free(gamma);
 
 	struct atomic atom;
-
 	atomic_begin(crtc, &atom);
 	atomic_add(&atom, crtc->id, crtc->props.gamma_lut, crtc->gamma_lut);
 	return atomic_end(drm->fd, &atom);
@@ -237,7 +236,7 @@ static uint32_t atomic_crtc_get_gamma_size(struct wlr_drm_backend *drm,
 		return 0;
 	}
 
-	return (uint32_t) gamma_lut_size;
+	return (uint32_t)gamma_lut_size;
 }
 
 const struct wlr_drm_interface atomic_iface = {

From dd69d7b7640fd4f957cee27eb274152cf8311f0c Mon Sep 17 00:00:00 2001
From: Vincent Vanlaer <vincent.vanlaer@skynet.be>
Date: Fri, 9 Feb 2018 19:37:01 +0100
Subject: [PATCH 7/8] Use VLA instead of heap alloc

---
 backend/drm/atomic.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/backend/drm/atomic.c b/backend/drm/atomic.c
index 10714e35..166d60a0 100644
--- a/backend/drm/atomic.c
+++ b/backend/drm/atomic.c
@@ -199,7 +199,7 @@ static bool atomic_crtc_move_cursor(struct wlr_drm_backend *drm,
 static bool atomic_crtc_set_gamma(struct wlr_drm_backend *drm,
 		struct wlr_drm_crtc *crtc, uint16_t *r, uint16_t *g, uint16_t *b,
 		uint32_t size) {
-	struct drm_color_lut *gamma = calloc(sizeof(struct drm_color_lut), size);
+	struct drm_color_lut gamma[size];
 
 	for (uint32_t i = 0; i < size; i++) {
 		gamma[i].red = r[i];
@@ -214,12 +214,9 @@ static bool atomic_crtc_set_gamma(struct wlr_drm_backend *drm,
 	if (drmModeCreatePropertyBlob(drm->fd, gamma,
 				sizeof(struct drm_color_lut) * size, &crtc->gamma_lut)) {
 		wlr_log_errno(L_ERROR, "Unable to create property blob");
-		free(gamma);
 		return false;
 	}
 
-	free(gamma);
-
 	struct atomic atom;
 	atomic_begin(crtc, &atom);
 	atomic_add(&atom, crtc->id, crtc->props.gamma_lut, crtc->gamma_lut);

From 7cb828ac70c0c41005a761d9011f8b0ca8904688 Mon Sep 17 00:00:00 2001
From: Vincent Vanlaer <vincent.vanlaer@skynet.be>
Date: Sat, 10 Feb 2018 10:24:49 +0100
Subject: [PATCH 8/8] Fallback gamma on legacy if properties don't exist

---
 backend/drm/atomic.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/backend/drm/atomic.c b/backend/drm/atomic.c
index 166d60a0..526b2731 100644
--- a/backend/drm/atomic.c
+++ b/backend/drm/atomic.c
@@ -201,6 +201,12 @@ static bool atomic_crtc_set_gamma(struct wlr_drm_backend *drm,
 		uint32_t size) {
 	struct drm_color_lut gamma[size];
 
+	// Fallback to legacy gamma interface when gamma properties are not available
+	// (can happen on older intel gpu's that support gamma but not degamma)
+	if (crtc->props.gamma_lut == 0) {
+		return legacy_iface.crtc_set_gamma(drm, crtc, r, g, b, size);
+	}
+
 	for (uint32_t i = 0; i < size; i++) {
 		gamma[i].red = r[i];
 		gamma[i].green = g[i];
@@ -227,6 +233,10 @@ static uint32_t atomic_crtc_get_gamma_size(struct wlr_drm_backend *drm,
 		struct wlr_drm_crtc *crtc) {
 	uint64_t gamma_lut_size;
 
+	if (crtc->props.gamma_lut_size == 0) {
+		return legacy_iface.crtc_get_gamma_size(drm, crtc);
+	}
+
 	if (!wlr_drm_get_prop(drm->fd, crtc->id, crtc->props.gamma_lut_size,
 			   &gamma_lut_size)) {
 		wlr_log(L_ERROR, "Unable to get gamma lut size");